First, the combustion characteristics of plywood
Ordinary plywood is a flammable material. When the ambient temperature is suitable, carbonization, ignition and combustion will occur, and spontaneous combustion will not generally occur. Plywood rarely burns without flame when heated at low temperature for a long time.
The form of plywood combustion is a form of thermal decomposition combustion. When plywood is in contact with a fire source, it is heated to evaporate water, generate heat, and precipitate some nonflammable gases. Then the outer layer began to decompose combustible gases, mainly hydrogen and methane, and at the same time released heat, which began to be strongly oxidized and produced flame combustion. When the wood that makes up plywood is completely decomposed, the flaming combustion will stop and turn to the flameless combustion stage. When plywood burns violently, high temperature and lack of oxygen will produce a lot of carbon monoxide, which is the main danger of fire. In addition, when other gases produced by combustion combine with water vapor, they form strong irritants, which directly endanger people's lives.
Second, the flame retardant treatment of plywood
Flame retardant treatment refers to the slow carbonization of plywood after flame retardant treatment, which can effectively prevent the spread of flame, inhibit the generation rate of harmful gases, and reduce it to the lowest degree, or leave the fire without smoldering.
To solve the flame retardant problem of plywood, we should first pay attention to solving the following problems. First, keep the original decoration, and the treated plywood should be suitable for all kinds of decoration. Second, the main physical and mechanical properties meet the use requirements. Third, it is easy to process. In addition, it should have little or no corrosiveness to metals. Any treatment should meet these requirements.
(1) flame retardant treatment method
At present, there are three kinds of flame retardant treatment processes for plywood abroad, namely, impregnation method, lamination method and coating method.
1, impregnation method
The flame retardant impregnating solution is impregnated into the molded plywood by pressurizing (or depressurizing), and dried and cured.
2. Lamination method
The flame retardant is added into the adhesive to make the flame retardant plywood, and then it is glued, assembled and hot pressed to make the flame retardant plywood. This method requires the panel to be very thin, and the thickness is below1mm. For example, urea-formaldehyde resin, melamine resin, resorcinol resin and the like are used. Add red phosphorus and halide (such as antimony chloride, tetrabromopropane, etc.). ) into these resins themselves or their mixed resins, and the veneer is pressed into flame retardant plywood with this adhesive.
3. Coating method (surface treatment method)
Brush or spray the prepared flame retardant liquid or various fire retardant coatings on the surface of plywood, and then dry it naturally or artificially. You can apply it as many times as you need.
Based on the above methods, the equipment of impregnation method is complicated, the flame retardancy of the plate produced by lamination method is not very good, and the decorative effect of coating method is not very ideal. In order to make plywood flame retardant and keep the original texture of wood, and overcome some shortcomings of the above treatment methods, impregnation lamination method has been studied in China. It uses the method of dipping the panel first and then brushing the flame retardant glue to manufacture the flame retardant plywood.
The first is effective flame retardant components, such as borides, phosphides, halides, etc. And adding a proper amount of penetrant, it is made into impregnating solution under certain conditions. After impregnation, the flame retardant penetrated into the cell cavity, cell wall and cell gap of wood, and the flame retardant veneer was obtained. Then, a flame retardant adhesive was prepared. According to the invention, a high-molecular phosphorus-containing compound which is insoluble (or insoluble) in water and does not react with the adhesive under certain conditions is selected as the main flame retardant of the flame-retardant adhesive, and a proper amount of auxiliary flame retardant and reinforcing agent are added and mixed evenly in the adhesive to prepare the flame-retardant adhesive. Glue coating, blank assembly and hot pressing forming.
The flame-retardant plywood produced by this method has the advantages of simple process, excellent flame-retardant performance, good decoration and wide application range in www.conran.com.cn.
(2) Flame retardant treatment agent
At present, the flame retardants used for plywood and other wood products are roughly as follows:
1, boride: It is an inorganic flame retardant with many varieties. Mainly zinc borate, barium metaborate, boric acid, borax, ammonium fluoroborate and so on. These compounds will generate solid solution at high temperature, which will coat the surface of the material, isolate the air and promote carbonization.
2. Phosphate: Phosphorus-containing compounds can be divided into two categories: inorganic and organic. Inorganic flame retardants mainly include ammonium polyphosphate, ammonium dihydrogen phosphate, guanidine phosphate and ammonium hexafluorophosphate. Organic flame retardants mainly include trihydroxypropyl phosphate, tetramethyl phosphate and triphosphate. There are many kinds of phosphorus-containing compounds, which are widely used. They can promote carbonization and prevent the flame from spreading at high temperature.
3. Halogen compounds: Halogen-containing flame retardants are mostly organic halides, such as tetrabromobisphenol A, tetrabromopropane and various halogenated phosphates. Inorganic flame retardants include zinc chloride, antimony chloride and ammonium bromide. They can generate hydrogen halide at high temperature, and react with active free radicals generated in the combustion process to generate groups with poor activity, thus preventing the chain reaction and reducing the combustion rate.